Conventional cigarettes include a column of smokable material, usually shredded tobacco material, wrapped in a combustible, air permeable paper wrapper. A filter, such as an acetate tow filter, is often wrapped in a substantially air-impermeable plug wrap paper, and is attached to an end of the wrapped tobacco column by tipping paper. As stated in Colin L. Browne's "The Design of Cigarettes," Hoechst Celanese Corporation, copyright 1990, the typical blended cigarette in the United States is either 85 mm or 100 mm in length with a diameter of about 8 mm. These cigarettes typically include a tobacco column of about 60 mm to 65 mm in length.
A typical cigarette contains 750 mg to 800 mg of tobacco. Approximately 20 mg of this tobacco is burned during a puff, while approximately 50 mg is consumed between puffs. The smoke generated by the burning tobacco during a puff is termed "mainstream smoke," while the smoke generated between puffs is termed "sidestream smoke." Since a large portion of the tobacco is wasted during quiescent periods between puffs, some manufacturers have attempted to reduce the combustion of tobacco during these quiescent periods.
One technique for reducing the sidestream smoke of cigarettes involves adding a burn modifier to the cigarette wrapper paper. Various compounds may be added to the cigarette wrapper paper to affect the sidestream smoke level. Commonly assigned U.S. Pat. No. 5,152,304, for example, indicates that the use of an acidic salt added to the cigarette wrapper paper reduces sidestream smoke.
Another technique for reducing sidestream smoke generally involves restricting the supply of oxygen to the tobacco column. For instance, commonly assigned U.S. Pat. No. 5,592,955 discloses disposing a tobacco column in a reusable, non-combustible, air-permeable shell. A filter is attached to one end of the shell by inserting the shell into a shell wrapper that is preattached to the filter by tipping paper. The shell reduces combustion between puffs, thereby reducing sidestream smoke, yet permits sufficient air flow to the lit tobacco column to avoid extinguishing the column. Commonly assigned U.S. application Ser. No. 09/003,497, filed on Jan. 6, 1998, discloses disposing a tobacco column in a laminated wrapper comprising a layer of aluminum foil sandwiched between two layers of paper. The wrapper restricts the flow of air to the tobacco column. A carbon ignition element is disposed within the tobacco column. The ignition element, in conjunction with perforations formed in the laminated wrapper, prevent the cigarette from extinguishing between normal puffs.
While several different techniques for reducing sidestream smoke have been proposed, there exists a need for additional effective techniques for reducing sidestream smoke.